1. Field of Invention
The present invention relates to an optical sorting system. More particularly, the present invention relates to a wafer ID optical sorting system employed in the semiconductor fabrication process.
2. Description of Related Art
Wafers 10, 20 fabricated in the semiconductor fabrication process each have their own IDs 12, 22, which are located opposite the notch 14 or the flat 24, as shown in FIG. 1. The IDs 12, 22 contain a lot number and a barcode, and are formed on the wafers 10, 20 by a laser. The IDs 12, 22 of each wafer 10, 20 are different from each other to allow easy recognition of the wafers 10, 20.
When an entire lot of wafers has completed a semiconductor fabrication process, sometimes a portion of the wafers does not meet the process requirements for, for example, film deposition or removal of photoresist. Therefore, a sorter machine with an auto ID reader is used to recognize automatically the ID of the wafer, such that trouble shooting can be performed. However, the auto ID reader may fail to read the ID when the photoresist or the material formed on the ID cannot be completely exposed or etched in such processes as wafer edge exposure or edge clamp process variation, resulting in wafer edge color difference. These various imperfections render the auto ID reader unable to clearly identify the ID.
In addition, if the ID is retrieved from the chamber and then identified by the naked eye, the wafer ID cannot be clearly recognized and the wafer is easily contaminated with particles. Additionally, the larger the wafer is, the more difficult it is to draw out and store, so that it is necessary to pay more attention to prevent the wafer from falling when the wafer is in operation. Accordingly, the cycle time in operation is increased and performance is decreased.